The present invention is directed, in general, to wireless communications systems and, more specifically, to methods for optimizing an uplink power window associated with radio receivers.
In a wireless communication system, an xe2x80x9cuplinkxe2x80x9d is a radio path (channel or link) over which a transmitter, such as in a Mobile Station (MS) sends encoded voice or signaling information to a radio base station (RBS) using modulated radio signals. Field observations have shown that interference levels at a cell level in a radio network are not static, but vary due to changes in the traffic load throughout a day, and from day to day. A high interference level during peak traffic periods statistically results in a low carrier-to-interference (C/I) ratio at a system level if all MSs transmit at a constant power level. A low C/I ratio directly results in degradation of network performance whenever the interference level in the system is increased.
A radio receiver has an uplink power window that defines upper and lower limits of received signal strength; i.e., a received signal must be within the uplink power window to be processed by the receiver. The uplink power window is designed to guide transmitters, such as in a MS, to transmit at an optimal power level that ensures a reliable radio link and a minimum disturbance to co-channels. In conventional wireless communications networks, the uplink power window for a Base Transceiver Station s (BTS) in each cell is defined by the system operator. Current implementations of uplink power window regulation require the system operator to manually define upper and lower limits of the power window for each cell. Once defined, the size and the lower baseline of an uplink power window are fixed, regardless of how the RF environment changes in each cell. If the strength of a received signal is outside the uplink power window, the BTS notifies the MS to adjust its transmit power level so that the received signal strength is expected to fall within the uplink power window.
There are several disadvantages to the use of a fixed uplink power window. First, the uplink power window can not be adaptively adjusted in response to changes in the RF environment. Second, manual adjustment of the uplink power window for each BTS in a cellular system requires extensive labor, resulting in increased operation and maintenance expenses. Furthermore, manual adjustment of the uplink power window can not provide an optimal adjustment, because any fixed uplink power window setting necessarily neglects short-term RF variations such as increased interference levels during peak traffic periods.
Accordingly, there is a need in the art for methods to optimize a radio receiver uplink power window. Preferably, such methods should be responsive to slow or fast variations in interference levels, and should be readily adaptable to implementation in the existing architecture of wireless communications systems.
To address the above-discussed deficiencies of the prior art, the present invention relates to methods for optimizing an uplink power window associated with a radio receiver, wherein the uplink power window is defined by upper (PU) and lower (PL) power levels. The methods disclosed herein provide an adaptive method of adjusting an uplink power window in order to effectively minimize uplink interference while maintaining satisfactory quality of service.
In an exemplary embodiment, the method comprises the basic steps of: i) determining a carrier signal strength (C) and an interference level (I); ii) calculating a carrier-to-interference ratio (C/I); iii) comparing the carrier-to-interference ratio (C/I) to a predefined target value; and iv) if the carrier-to-interference ratio (C/I) is less than the predefined target value, increasing the size of said uplink power window, otherwise, if the carrier-to-interference ratio (C/I) is greater than the predefined target value, decreasing the size of the uplink power window.
In a preferred embodiment, the step of increasing the size of the uplink power window can include the step of increasing the upper (PU) power level; in alternate embodiments, the step of increasing the size of the uplink power Window can include the step of decreasing the lower (PL) power level, or increasing the upper (PU) power level in combination with decreasing the lower (PL) power level. In related embodiments, the step of decreasing the size of the uplink power window can include the step of decreasing the upper (PU) power level; in alternate embodiments, the step of decreasing the size of the uplink power window can include the step of increasing the lower (PL) power level, or decreasing the upper (PU) power level in combination with increasing the lower (PL) power level.
In an exemplary embodiment, the step of determining a carrier signal strength (C) includes the steps of: i) collecting a plurality of sample values of the carrier signal strength over a period (T); and ii) computing the carrier signal strength (C) as a function of the plurality of sample values. The step of computing the carrier signal strength (C) as a function of the plurality of samples can include the step of calculating an average value of the plurality of sample values of the carrier signal (Cavg) or, alternatively, can include the step of calculating a Cumulative Distribution Function of the plurality of sample values of the carrier signal (CCDF). In related embodiments, the step of determining an interference level (I) includes the steps of: i) collecting a plurality of sample values of the interference level (I) over a period (T); and ii) computing the interference level (I) as a function of the plurality of sample values. The step of computing the interference level (I) as a function of the plurality of samples can include the step of calculating an average value of the plurality of sample values of the interference level (Iavg) or, alternatively, can include the step of calculating a Cumulative Distribution Function of the plurality of sample values of the interference level (ICDF).
In some embodiments, the size of the uplink power window can be limited by predefined maximum (PMAX) and minimum (PMIN) values. In such embodiment;, the step of increasing the size of the uplink power window is preferably bypassed if the size of the uplink power window is equal to the predefined maximum (PMAX) value; similarly, the step of decreasing the size of the uplink power window is preferably bypassed if the size of the uplink power window is equal to the predefined minimum (PMIN) value.
The foregoing has outlined, rather broadly, the principles of the present invention so that those skilled in the art may better understand the detailed description of the exemplary embodiments that follow. Those skilled in the art should appreciate that they can readily use the disclosed conception and exemplary embodiments as a basis for designing or modifying other structures and methods for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.